Glycated Hemoglobin: What is it? What is its Importance? Test, Levels and Related Conditions

People with Diabetes must control the disease to avoid complications.

The term “glycated hemoglobin” refers to glycated hemoglobin. It develops when hemoglobin, a protein within red blood cells that carries oxygen throughout the body, binds to glucose in the blood, becoming ‘glycosylated.’

By measuring glycated hemoglobin (HbA1c), doctors can get a general idea of ​​our average blood sugar levels over weeks/months.

For people with Diabetes, this is important as the higher the HbA1c, the greater the risk of developing diabetes-related complications.

Your doctor may want to test your blood sugar levels daily at certain times of the day. There is a medical test known as capillary blood glucose.

“Glycated hemoglobin,” also called glycated hemoglobin, hemoglobin A1c, or HbA1c, supplements the information from the other tests. The doctor uses it to determine if additional measures should be taken to avoid possible complications.

We can define it as the measurement of blood glucose levels in the last three months.


¿Why is it so important?

To understand its importance, you need to know that the red corpuscles in your body are made up of a part of hemoglobin (a protein).

At the same time, the glucose that travels through the bloodstream can adhere to hemoglobin for a time interval between 90 and 120 days (that is, roughly the equivalent of three months).


  • If they are no levels greater than 6.5%, the person has Diabetes.
  • If they are between 5.7% – 6.4%, the person is in a prediabetes stage.
  • If they are less than 5.7%, the person does not have Diabetes.

You should know that these results are only a guide. Depending on the type of Diabetes supported, these percentages may vary slightly.

How often should the test be done?

It is preferable to repeat the test every three months so that the doctor can know if the diabetes monitoring carried out by the patient was carried out correctly or not.

This test allows us to have a retrospective perspective of the monitoring of the disease.

Glycated hemoglobin test (HbA1c)

The non-enzymatic glycation of hemoglobin produces glycosylated hemoglobin (HbA1c). The degree of glycation reflects the mean plasma glucose during the life of the red blood cells (approximately three months).

The HbA1c test is attractive as it measures chronic blood glucose rather than instant blood glucose. It has been used as an objective marker of average glycemic control for many years and has an accepted place in managing patients with Diabetes.

The HbA1c test provides significant practical advantages over blood glucose measurement. It can be performed at any time of the day and does not require any special prior preparation from the patient.

The blood sample is stable once collected, essentially in the same tube used for a complete blood count.

When access to an appropriate laboratory is limited, testing can be performed using a point-of-care testing machine. This can be particularly useful in rural and remote areas.

How does the HBA1c return an accurate average blood glucose measurement?

When the body processes sugar, glucose in the bloodstream naturally attaches to hemoglobin. The amount of glucose that combines with this protein is directly proportional to the total amount of sugar in your system.

Because red blood cells in the human body survive for 8-12 weeks before renewal, measuring glycated hemoglobin (or HbA1c) can be used to reflect the average levels of glucose in the blood during that time.

This provides a valuable indicator of longer-term blood glucose control. If your blood sugar levels have been high in the last few weeks, your HbA1c will also be higher.


The HbA1c goal for people with Diabetes is:

  • 48 mmol / mol (6.5%).

Please note that this is a general goal and that people with Diabetes should be given an individual plan that their healthcare team can target.

An individual HbA1c should consider your ability to reach the goal based on your day-to-day life and whether you are at risk for severe or regular hypoglycemia.


Two extensive studies: the UK Prospective Diabetes Study (UKPDS) and the Diabetes Control and Complications Trial (DCCT), showed that HbA1c improves by 1% (or 11 mmol/mol) for people with type 1 diabetes or type 2 diabetes, the risk of microvascular complications by 25%.

Microvascular complications include:

Research has also shown that people with type 2 diabetes who lower their HbA1c by 1% are:

  • Suffer from heart failure
  • 43% less likely to suffer amputation or death due to peripheral vascular disease.

When Should HbA1c Levels Be Tested?

All people with Diabetes mellitus in the UK should be offered an HbA1c test at least once a year.

Some people may have an HbA1c test more often. This may be more likely if your medications have recently been changed or if your healthcare team wants to monitor your diabetes control more than once a year.

How do blood glucose levels compare to HbA1c readings?

The table (Figure 2) shows how average blood sugar levels in mmol / L will translate into HbA1c readings and vice versa.

It is essential to know that because blood glucose levels are constantly fluctuating, blood glucose tests are required to understand how levels change throughout the day and learn how meals affect your glucose levels.

Glycated hemoglobin (HbA1c) laboratory tests diagnose diabetes mellitus and assess control Diabetes mellitus.

Hemoglobin A1 and Hemoglobin A1c

Chromatography of normal adult blood is divided into two parts:

  • HbA (HbA0) 92-94%.
  • HbA1 (6-8%), where the B chain has an additional glucose group.

HbA1 itself consists of three different glycations, with the HbA1c subgroup being the most useful, generally measured by isoelectric focusing or electrophoresis.

Hemoglobin glycation occurs at a variable rate (non-linear rate) over time throughout the life of the red blood cell (RBC), which is typically 120 days.

This means that the relative proportion of glycated hemoglobin at any given time depends on the average glucose level during the previous 120 days.

Normal levels (routine laboratory “range”) will vary depending on whether HbA1 or HbA1c is measured and the method used.

HbA1c is usually a reliable indicator of diabetes control, except in situations where the half-life of red blood cells is significantly less than 120 days.

They will generally lead to low HbA1c results because 50% of glycosylation occurs on days 90-120.


Increased blood cell turnover: blood loss, hemolysis, hemoglobinopathies, red blood cell disorders, myelodysplastic disease.

Interference with the test (this depends on the method used: persistent fetal hemoglobin and hemoglobin variants, carbamylated hemoglobin in uremic patients).

In patients with very high and deficient levels, HbA1c readings can be misleading (the physician must compare with additional information obtained from home capillary blood glucose tests).

HbA1c can be very helpful in identifying patients who may be reporting unrealistically good home glucose testing.


Although the HbA1c test is used primarily to monitor blood sugar control in patients with Diabetes, the World Health Organization (WHO) now recommends that HbA1c be used as a diagnostic test for Diabetes.

This is provided that there are rigorous quality-control tests and that the analyzes are standardized to criteria aligned with international reference values.

An HbA1c of 48 mmol/mol (6.5%) is recommended as a cut-off point for the diagnosis of Diabetes.

A value less than 48 mmol/mol (6.5%) does not exclude diabetes diagnosed by glucose tests. An advantage of using HbA1c for diagnosis is that the test does not require a fasting blood sample.

Situations in which HbA1c is not appropriate for the diagnosis of diabetes include:

  • Children and youth.
  • Patients suspected of having type 1 diabetes
  • The pregnancy.
  • Patients with symptoms of Diabetes for less than two months.
  • Patients at high risk for Diabetes are acutely ill.
  • Patients take medications that can cause a rapid rise in glucose, e.g., steroids and antipsychotics.
  • Patients with acute pancreatic damage, including pancreatic surgery.

Presence of other factors that influence HbA1c and its measurement:


  • Increased HbA1c: iron deficiency, vitamin B12 deficiency, decreased erythropoiesis.
  • HbA1c decrease: administration of erythropoietin, iron, vitamin B12, reticulocytosis, chronic liver disease.

Altered Hemoglobin

  • Genetic or chemical alterations in hemoglobin: hemoglobinopathies, HbF, and methemoglobin can increase or decrease HbA1c.


  • HbA1c increase: alcoholism, chronic kidney disease.
  • Decrease in HbA1c: aspirin, vitamin C, and vitamin E, certain hemoglobinopathies.

Destruction of erythrocytes

  • Increased HbA1c – The increased life span of erythrocytes, e.g., splenectomy.
  • HbA1c  decreased – Red blood cell lifespan decreased, for example, hemoglobinopathies, splenomegaly, rheumatoid arthritis, or medications such as antiretrovirals, ribavirin, and dapsone.

Other factors:

  • Increased HbA1c: hyperbilirubinemia, alcoholism, large doses of aspirin, chronic use of opiates.
  • Variable HbA1c: hemoglobinopathies.
  • HbA1c decrease: hypertriglyceridemia.